Nagle should be turned off for protocols that use a lot of small-sized (at TCP/HTTP level) messages. I don't think it's ok to do this always.

Please also note WCF does not necessarily means SOAP. It depends on the bindings used. The message size also depends on the encoding used. WCF is very configurable.

WCF can use for example JSON. So let's say you build a server application on WCF+JSON+REST, and the average JSON payload is small (say, less than 1500 bytes, which means ~1500 characters since JSON is using UTF-8 by default), than, it's probably worth it.

But, if your application is using a SOAP binding and you measure that the average message size is more than 1500 bytes (which seems frankly possible with SOAP XML payloads), than it's not worth it.

So, you really need to measure things before taking a decision IMHO - like the Azure guys did, well, maybe they did it after :-). One simple way to measure HTTP message size is to use Fiddler2, especially the statistics tabs (select all message, it will give you the total number of frames, and the total number of bytes).